And for anyone else interested here's a person on irc teaching me (thanks)

[00:10] <me> to know how they find extrasolar planets
[00:10] <X> Oh, well that's a simple enough conversation we can have right here.
[00:10] <me> thank you
[00:11] <me> i assume its simple newtonian physics
[00:11] <X> Does the word "photometry" mean anything to you?
[00:11] <me> i understand the basics
[00:11] <X> Of?
[00:12] <me> well they measure the movement of the star then build a computer model to account for the variation in movement of the stars averaged path
[00:12] <me> and adjust so that the orbiting planet makes it fit better to the 'wobble'
[00:12] <me> then add smaller bodies gradually until you get a very near fit
[00:12] <me> am i right?
[00:12] <X> Mostly ;)
[00:12] <X> How do you suppose the movement is measured?
[00:13] * zzz needs a dob mount..
[00:13] <X> You do.
[00:13] <me> looking at the star?
[00:14] <me> i made a star system simulator with where you can create bodies and they orbit each other, so that'd be my base
[00:14] <me> (thanks for your help btw ;)
[00:14] <X> Well, it turns out the a Jupiter sized planet only tugs at its star hard enough to move it a few tens of meters (maybe even less, I think).
[00:15] <X> Since stars are so far away that we can't even resolve their surfaces without some very exotic methods, we're very unlikely to _visually_ observe the wobble of a star.
[00:15] <me> fyi kepler released loads of star data for free download (scroll down to my post) https://www.physicsforums.com/showthread.php?t=410442
[00:15] <X> So, it must be something else ;)
[00:15] <me> yep figured
[00:15] <X> Yes. And much, much more coming in the future.
[00:15] <me> very exciting :)
[00:16] <X> Do the terms "redshift" or "blueshift" mean anything to you?
[00:16] <me> yep the doppler effect
[00:16] <X> Alright.
[00:16] <me> but is that different?
[00:16] <X> Well, what makes an object's light undergo a doppler shift?
[00:17] <me> moving fast relative to us
[00:17] <X> Any special direction?
[00:17] <me> away outwards from the earth
[00:18] <X> So that would induce a redshift.
[00:18] <X> Blueshift is the opposie.
[00:18] <X> Well anyway, it turns out that if we measure a star's spectra, we can see very minute changes where the lines move subtly back and forth.
[00:19] <allenk> I experience doppler shift every day.
[00:19] <X> We're able to do this accurately enough that we can see a planet's very minute influence upon a star.
[00:19] <me> oh wow
[00:19] <X> So that's _one_ method.
[00:19] <me> so we can see all directions
[00:19] <X> Well, that method has a weakness.
[00:19] <X> Imagine a planet cruising around its star.
[00:20] --> caramel has joined this channel (~mel@wrongplanet/caramel).
[00:20] <X> It gently tugs the star in its direction as it goes around, right?
[00:20] <-- linear_shift has left this server (Ping timeout: 260 seconds).
[00:20] <me> ok
[00:20] <-- linear_shift_p4 has left this server (Ping timeout: 264 seconds).
[00:20] <X> Imagine that you're looking at a plate or a CD edge on.
[00:20] <X> If that planet is happily charging around the edge of the lpate, the star in the middle will be pulled toward you at one point and pushed away at another.
[00:21] <X> Do you agree?
[00:21] <me> yes
[00:21] <X> Well, what happens if we see the plate face on?
[00:21] <X> Are we likely to see the star being pulled toward us or pushed away?
[00:21] <me> the star dims
[00:22] <me> oh
[00:22] <me> pulled away
[00:23] <me> not enough light when being pulled towards us
[00:23] <X> This is you: \o/
[00:23] <X> [19:20:26] <X> Imagine that you're looking at a plate or a CD edge on.
[00:23] <X> [19:20:55] <X> If that planet is happily charging around the edge of the lpate, the star in the middle will be pulled toward you at one point and pushed away at another.
[00:23] <X> This is you and the plate: \o/ |
[00:23] <X> Er, hang on.
[00:23] <X> [19:20:26] <X> Imagine that you're looking at a plate or a CD edge on.
[00:23] <X> [19:20:55] <X> If that planet is happily charging around the edge of the lpate, the star in the middle will be pulled toward you at one point and pushed away at another.
[00:23] <X> This is you and the plate: \o/ -
[00:23] <X> In that situation, we agreed that the star would move back and forth relative to you.
[00:24] <X> What about this situation? \o/ |
[00:24] <me> nothing?
[00:24] <X> Why do you say that?
[00:24] <me> i mean no redshift
[00:24] <X> Why do you say that?
[00:24] <me> we're viewing the disk from birds eye
[00:25] <X> ...so?
[00:25] <me> it moves up and down but not in and out
[00:25] <X> :)
[00:25] <X> Which would be very upsetting to Alex DeLarge.
[00:25] <me> why is this a problem though?
[00:26] <X> Can you detect an exoplanet if its orbit is in that orientation with this method?
[00:26] <me> not if you rely on the redshift method :(
[00:26] <me> but cant you measure the physical movement of that pixel?
[00:27] <X> Of the star?
[00:27] <me> yep
[00:27] <X> So what you're describing is the "astrometry" method of detecting an exoplanet.
[00:27] <X> We've done that with binary stars for ages, but it's only worked with an exoplanet ONCE.
[00:27] <X> And even then, we're still waiting to confirm that one.
[00:28] <me> i see. very difficult.
[00:28] <me> thanks for explaining this to me ;) and the link is very good too
[00:28] <X> Sure.
[00:29] <X> I strongly recommend that you read or ask about the photometric method so you can understand what Kepler is doing.

Staff: Mentor

I stopped reading shortly after "Does the word "photometry" mean anything to you?"

It appears not...

Photometry is using a telescope and ccd camera to measure the brightness of an object. So then the most common method is to take continuous measurements of the brightness of a star and detect periodic changes in that brightness. If the star is not a known variable and the brightness occasionally drops, there is a good chance that the drop is due to the existence of a planet.

So you don't need any data to confirm the existence of such a planet, just a foreknowledge of if such a planet has already been found around a star you are looking at. Calculating properties is a little more difficult (but not too difficult) and is where Newton comes in. If you know the mass of the star and the period of the transits, you can calculate the orbital distance. If you know the brightness of the star and measure the brightness change, you can calculate the size of the planet.

yep thanks that works too. But afaik you have to be coplanar with the star-planets orbit which is rare. the method I was asking about was the one using the wobble in a stars movement (away and towards the viewer).

Basically, you can detect and determine characteristics of an existing planet. providing that your instruments are sensitive enough and the planet not too small. This workd basically for any orbit except one that is normal to the line-of-sight path from us. It takes allowance of the fact that the star and planet are a two-body system, and they might be described to orbit each other - - - like a spinning dumbbel, in which one mass is usually considerably larger than the other. In other words, the system turns about a point usually somewhere inside the star, but not at its center of mass. This means that the star itself is pivoting around that point, and as long as that motion is not normal to our sight line - - - it means that the star is moving toward us for a while, then away for a while, and so on.

This all results in a continual shift in frequencies of the spectral lines of that star (doppler shift). This shift, along with the considerations Russ gave, allow the planet's parameters to be calculated, if it isn't too small to make out.

If the orbit is normal, to us, calculation can still possibly be made, by measuring the star's lateral shift, but this is often not so easy.